The Roman salute

Maybe because it's the longest digit, sticks up the farthest already. But the bird is so old a gesture, there's no way of proving that. The Gesture King, the guy who wrote the book, is British anthropologist Desmond Morris. He says the first references to it that still exist are in Roman literature. Very popular back in the day, apparently. It was called the "impudent digit" and had the same meaning then as it does now. The best speculation relates the gesture to the obvious, an erect penis, which in Roman times was a magical symbol thought to ward off evil. Indeed.